Modeling lactate threshold in cycling—influence of sex, maximal oxygen uptake, and cost of cycling in young athletes

Abstract

Purpose Understanding physiological determinants of lactate threshold 2 (LT2) is crucial for tracking adaptations and deriving individualized training recommendations in cycling. Therefore, the study investigated: 1. the accuracy of modeling power output at LT2 in young athletes of both sexes using maximal oxygen uptake ( $${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$ V ˙ O 2 peak ), fractional utilization of $${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$ V ˙ O 2 peak (% $${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$ V ˙ O 2 peak ), and oxygen cost of cycling (Cc); 2. the influence of Cc determination on the model accuracy; 3. the influence of the model predictors and inclusion of maximal lactate accumulation rate ( $${\dot{c}}La_\textrm{max}$$ c ˙ L a max ) on power at LT2 depending on sex. Methods Eighty-three cyclists and triathletes (22 females, 61 males; age [median and IQR]: 14.6 [13.8–17.6] years, $${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$ V ˙ O 2 peak [mean ± SD]: 59.2 ± 6.5 mL⋅kg –1 ⋅min –1 ) performed an incremental test to determine power at LT2, $${\dot{V}}\textrm{O}_{2_\textrm{peak}},$$ V ˙ O 2 peak , % $${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$ V ˙ O 2 peak at LT2, and Cc (assessed at 3 W⋅kg –1 , 75% $${\dot{V}}\textrm{O}_{2_\textrm{peak}},$$ V ˙ O 2 peak , and 90% LT2). Results Modeled and experimentally determined power at LT2 demonstrated excellent agreement for all, male and female athletes (ICC $$\ge$$ ≥ 0.961), with Cc at 90% LT2 providing the highest accuracy (ICC $$\ge$$ ≥ 0.986). The three physiological determinants explained $$\ge$$ ≥ 98% of the variance in power at LT2, with the largest unique contribution from $${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$ V ˙ O 2 peak (62 and 67% of total $$R^2$$ R 2 ), followed by Cc (8 and 34%) and % $${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$ V ˙ O 2 peak at LT2 (5 and 12%) in males and females, respectively, while $${\dot{c}}La_\textrm{max}$$ c ˙ L a max did not improve the regression. Conclusion $${\dot{V}}\textrm{O}_{2_\textrm{peak}}, $$ V ˙ O 2 peak , % $${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$ V ˙ O 2 peak at LT2 and Cc accurately predict power at LT2 in young cycling athletes independent of sex, with determination of Cc at 90% LT2 providing the highest accuracy. While $${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$ V ˙ O 2 peak contributes most to LT2 in both sexes, Cc appears more important in young females.

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